Exhaust gas catalytic converters can advantageously improve the exhaust gases of internal combustion engines, in a manner known per se, by the fact that harmful constituents of the exhaust gas are converted into less harmful constituents by catalytic conversion. It is known that an exhaust gas catalytic converter requires a minimum operating temperature for this. Below this minimum operating temperature the effect of the exhaust gas catalytic converter is low or not present at all. This is important, for example, in an idle mode after a cold start of the internal combustion engine.